Machine for obtaining metal castings

ABSTRACT

A method for providing metal castings by using disposable wax dies, comprising through a predetermined and completely automatic cycle a previous degassing step of the die by sucking from the bottom and then the pouring step of the molten metal by a combination of suction from the bottom and pressure from the top on said die, the pressure being applied when degassing approaches the molten metal in the die pot.

[56] References Cited UNITED STATES PATENTS Via De Pretls 5, Pavia; Giancarlo Dal Pra, Via Matteotti 2,

United States Patent [72] inventors UgoBarhleri no 88000 O 00O6 3 3 333 O/O/l/ 2343444 l 6 666 44l4lll. 6e 6 w m wk mm m .r n it amauh h HSSPHPWF lllllll Rllillizz v.

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N mw L n n ew flafl AFPP 1111]] 2523 224333 iliiii Primary Examiner-J. Spencer Overholser Assistant E.\'aminerV. K. Rising Auomey Karl W. Flocks ABSTRACT: A method for providing metal castings by using osable wax dies, comprising through a predetermined and pletely automatic cycle a previous degassing step of the die by sucking from the bottom and then the pouring step of the molten metal by a combination of suction from the bottom essure from the top on said die, the pressure being applied when degassing approaches the molten metal in the die r m p P d L S mm m w 2mm 1 mw mm S $8 1 A 0"} c mw m L m mm m 1 72% E w m mw HF mfimm M w m: R m mm mm T F3" "N E m S we mm m a L0 CG d A05 LM M U F M U H 0 5 H mm MACHINE FOR OBTAINING METAL CASTINGS This invention relates to a method and a machine for obtaining metal castings, method and machine which may be regarded for general use, while being particularly applied in the jewelry and odontology art.

Machines are known for casting precious and nonprecious metals, in which machines the cast metal to be introduced into a disposable wax die is introduced by pressure or vacuum, or both simultaneously.

The methods and machines which have been hitherto used have substantial drawbacks and do not allow to obtain highquality castings. Thus, the use of pressure alone to supply the molten metal to the die may build up a swirl effect in the mo]- ten metal and accordingly cause blisters or other defects to be formed in the finished casting. It is known that the dies being used for casting by the disposable wax method are preheated at a temperature near the melting temperature for the metal used; at this temperature, the materials used for die forming would evolve gases which when entering the casting, would provide defects in the finished piece. In order to remove such defects, the die should be degasified, which is surely impossible if the molten metal is forced into the die as a result of pressure alone. Although allowing a sufficient die degassing, the use of vacuum alone would, however, not allow to obtain castings having a good reproduction in details or castings having extremely thin portions, in connection with the inherent difficulties in providing a high vacuum. Further, large passage holes are required for the molten metal, after all causing a substantial waste of metal material.

The simultaneous use of pressure and vacuum may theoretically remove the drawbacks mentioned above, but hitherto a correct use thereof has not been made and therefore has caused the same drawbacks as in the above-cited techniques. Thus, by simultaneously applying pressure and vacuum, the die cannot be completely degassed at its top portions and therefore blisters will still be formed in the finished piece. Moreover, the prior art machines are manually controlled by an operator, which further increases the chances of low-quality castings.

Thus, the operator might by mistake delay the vacuum application and, accordingly, the casting would substantially occur by pressure or, on the other hand, the operator might delay the pressure application and in this case the casting would substantially occur under vacuum. Obviously, in both of these cases, the same drawbacks as found in the above-cited vacuum or pressure casting, would be present.

Further, by committing the machine operation to manual control, one is bound to the operators skill who will necessarily affect the duration or times of the several steps of the machine working cycle that is to say, the operator is incapable of repeating the same times of a cycle which is believed as perfect, so that the castings will qualitatively differ from one another.

It is the object of the present invention to provide a method and a machine for obtaining metal castings, completely removing the drawbacks mentioned above because of a predetermination in the duration times for the several steps of the operating cycle, and various parameters, such as the shape and volume of the castings to be carried out.

The method according to the invention substantially comprises a degassing step of the die by vacuum alone and then a pouring step into the degassed die by simultaneous pressure and vacuum, the casting occuring only when degassing has approached the molten metal placed within the die pot. It is important to note that die degassing, proceeding from bottom to top, is continued to approach the molten metal in the pot or feedhead over the molten die without affecting the molten metal, as the latter would otherwise tend to enter the pouring channel, cooling down and partially obstructing it.

The machine for carrying out the above method substantially comprises a vacuum circuit and a pressure fluid circuit, and automatically operated valve means for accomplishing the sequence of the various cycle steps, as more clearly explained in the following.

These and further features of the invention will be more apparent referring to the accompanying drawings, showing by way of not limiting example a particular embodiment of the machine according to the invention.

In the drawings:

FIG. 1 is an elevational and partly sectional view showing the machine according to the present invention;

FIG. 2 is a sectional view showing a detail of the machine in FIG. I',and

FIG. 3 is the connection diagram for several members of the machine in FIG. 1.

Referring to the accompanying drawings, the machine will be first described in order that the operation thereof according to the claimed method may be understood.

REferring to FIG. I, it will be seen that the machine according to the present invention substantially comprises a base 1 for springy support of a lower disc 2, the latter supporting and sealing the lower end of die 3. More particularly, the lower disc 2 is resiliently supported at a given distance from base I by suitable springs 4 (of which only one is shown in FIG. I), each being guided by its own vertical spoke 5 which is secured to the lower face of disc 2 and capable of freely running within a suitable through hole in said base 1.

The lower disc 2 has one or more concentric seatings 6 for a die 3 and has also an axial bore 7 communicating the inside of die 3 with the vacuum circuit, as explained hereinafter. A filter 8, located at the top of bore 7, prevents any passage of solid particles in the case being separated from the die.

Laterally of the lower disc 2, an upright 9 is secured to base 1, at the upper end of this upright 9 an arm I0 being pivoted and horizontally movable from an operative position, wherein said arm is over the die, as shown in FIG. 1, and an inoperative position. More particularly, by an end thereof said arm I0 is secured to the corresponding end of a vertical shaft II, rotat ing internally of upright 9, at the other end of which is secured a projecting portion 12, the function of which will be explained in the following.

The free end of arm 10 carries a pneumatic cylinder [3 which is suitably supplied by a pressure fluid source. Cylinder I3 is vertically arranged and at the free end of its piston stem 14 a second disc I5 is loosely fitted and adapted to seal the upper end of die 3. More particularly, a bushing 16 is secured to the free end of stem 14 and has a rounded head I7 bearing with its curved surface against the upper face of disc I5. Further, the head I7 of bushing 16 is accommodated within a corresponding seat at the top of said disc I5, so that the latter may slightly swing to fit to any unevennesses in the upper surface of die 3.

The upper disc 15 is also provided with an axial blind bottom bore 18, communicating through a side passage I8 with the pressure fluid supply circuit (FIG. 3) for building up a pressure on the fluid metal in the pot 25 of die 3 to enable the fluid metal to enter said die, as explained hereinafter. A suitable filter 19, located at the lower end of bore I8, prevents the fluid from directly impinging the surface of the molten metal and thus giving rise to swirls. A handle 20 is secured to the free end of arm 10 to move the latter between its inoperative and operative positions, the operative position corresponding to that shown in FIG. 1, wherein the upper and lower discs 15 and 2, respectively are aligned with die 3.

Sidewise of base I two ears 2] and 22 are formed, wherein screws 23 and 24, respectively, are screwed. Screws 23 and 24 are located approximately on the centerline of base 1 and project slightly relative to its lower surface, so that the operator can slightly swing the whole machine to make sure if the metal within pot 25 over die 3 is completely molten.

As shown in FIG. 1, one or more channels 26, 26 derive from pot 25 of die 3 and serve for conveying the molten metal into the recesses 27, 27' associated with the article to be obtained as desired.

The machine according to the present invention is provided with a work-retaining means and a safety means. As shown in FIG. 2, illustrating a longitudinal section along a vertical at said projecting portion or feather 12, the work retaining means substantially comprises a ball 29 housed within a bore 30 of feather l2 and constantly urged by a spring 31, acting to urge the ball 29 upwards and against a proper seat 32 in the lower face of base 1 and at the operative position of movable arm 10. Thus, when said arm is moved to its operative position, the retaining means just described will prevent a lateral displacement thereof so as to minimize or almost completely eliminate operator's intervention, likely responsible, as known, of mistakes and undesired drawbacks. The second or safety-retaining means substantially comprises a projecting spoke 33 (schematically shown in FIG. 3) which prevents feather 12 from passing beyond the operative position, shown by full lines in FIG. 3, and thus damaging the valves controlled thereby, as explained hereinafter.

Referring to FIG. 3, the vacuum and pressure fluid circuits will be described.

The vacuum circuit substantially comprises a vacuum pump 34 connected to reservoir 35 which is connected in turn through duct 36 to an inlet of a dual control valve 37, manually operable and an outlet of which is connected through duct 39 to the inlet of a valve 39 which is operated by feather 12 when the latter is at its operative position, as shown by full lines in FIG. 3. in turn, the outlet of valve 39 is connected through duct 40 to bore 7 of lower disc 2 supporting the die 3 for vacuum building up and internal degassing thereof.

A vacuum gauge 41 is connected to the reservoir for indicating the vacuum degree being attained and an outlet 42 of valve 37 is for communicating the just-described vacuum circuit with the surroundings when said valve 37 is at inoperative position.

The pressure fluid circuit substantially comprises a pressure fluid source (not shown) which through duct 43 is connected to the second inlet of dual valve 37, the second outlet of which is connected through duct 44 to a T-union 45 for two pressure-reducing valves 46 and 47, respectively. The manually operable pressure reducing valve 46 is connected through a tube 48 to the inlet of second valve 49 also operated by feather 12. In turn, valve 49 is connected through a flow regulator 50 to cylinder 13 which controls the lowering of upper disc 15. As seen in FIG. 3, the pressure fluid supplied to cylinder 13 operates for lowering its piston and disc as well, while a spring 51 operates against the fluid pressure to retain the piston at raised position.

In turn, the manually operable pressure reducing valve 47 is connected to a valve 52 which is located underneath the lower disc 2 and operated by lowering thereof. In turn, valve 52 is connected through a flow regulator 53 to bore 18 of the upper disc 15 to convey the pressure fluid on the molten metal in pot 25. The gauges 54 and 55, respectively, for pressure valve indication are also connected to said pressure reducing valves 46 and 47.

The operation of the machine according to the invention will now be described. Assuming that the machine is at inoperative condition and more particularly that the movable arm 10 is rotated to its hatched position 12in FIG. 3; further, that the manually operated control valve 37 is closed for preventing vacuum and pressure fluid from entering the machine circuit. Under these conditions the piston of cylinder 13 is upward urged along with the upper disc 15 by spring 31 and, accordingly, the lower disc 2 is held at raised position by springs 4, so that the underlying valve 52 is closed.

At the beginning of pouring operations, the machine is set by opening valve 37, so as to preset the pressure fluid and vacuum circuits. The opening of manual valve 37 will not yet cause any operation of the machine since vacuum is stopped by valve 39, while the fluid is stopped by valve 49 in the direction of cylinder 13 and by valve 52 in the direction of the upper disc 15.

Having placed within pot 25 the metal to be melted and after bringing it to smelting, arm 10 is moved to its operative position so that feather 12 will simultaneously or subsequently operate valves 39 and 49. Thus, it should be specified that the position of valves 39 and 49, or the length of the stems thereof, can be suitable adjusted for causing a simultaneous or subsequent operation of said valves.

Opening of valve 39 will provide for vacuum within die 3, thus starting the degassing for the latter, this degassing gradually proceeding from bottom to top in the direction of pot 15.,

Simultaneously with degassing operation beginning, opening of valve 49 will cause pressure fluid to be supplied to cylinder 13, which will cause upper disc 15 to be lowered and, by descending, to bear on the upper face of die 3, sealing it and, accordingly, on continued descent it will urge the die 3 downwards along with the lower disc 2 until the latter impinges the stem of the underlying valve 52 and causes it to open. In all this period, and particularly from the moment the upper flange or disc begins to descend to the moment the lower flange or disc opens said valve 52, the die-degassing operation is carried out and the times are so selected that degassing will terminate just at pot 25 and at the moment opening of valve 52 occurs, which provides for pressure fluid supply to the upper disc 15 and, accordingly, on the molten metal.

From the foregoing, it should then be noted that pouring occurs both because of pressure fluid and vacuum, but after vacuum has degassed die beforehand. Thus, perfect reproductions of small details can be achieved and castings can be obtained as completely free of impurities.

Upon pouring completion, the metal is allowed to cool down within the die, so that it may be shaped, and then control valve 37 is closed, thereby releasing pressure fluid and vacuum supply and communicating the two circuits with the surroundings to provide for disc separation from the die. Arm 10 is then rotated to its inoperative position in order to start a next cycle again.

It is known that the die sizes may vary depending on the piece or pieces to be obtained. As a result, the power of cylinder 13 has to be varied for fitting the pressure exerted by the upper disc 15 on die 3 according to the upper face of said die, so that this pressure is enough for making up a sealing. In addition to this, the introduction of pressure fluid into cylinder 13 should be gradually adjusted through valve 50 to conform the descent time of the upper disc 15 to the actual length of die 3, so that the latter can be completely degassed prior to introduction of pressure fluid into the upper disc 15. This is achieved by adjusting the several valves in the circuit.

It should be understood that the foregoing, as described and shown in the accompanying drawings, has been given by mere way of not-limiting example and that further changes can be made to the method and machine according to the present invention, without departing for this from the covering field of the invention.

What is claimed is:

l. A machine for producing metal castings using disposable wax dies, comprising a supporting base supporting a first closing means vertically movable between upper and lower positions for supporting and sealing at the bottom a die, a second closing means vertically movable between upper and lower positions for sealing said die at the top and simultaneously urging the first closing means to the lower position, a pneumatic means for operating the second closing means of said die, the first and second closing means being connected, respectively, to a vacuum circuit and a pressure fluid circuit; the machine comprising first and second valve means, respectively, operable to supply vacuum to the first closing means for purposes of degassing said die and to supply pressure fluid to said pneumatic means for operating the second closing means, and also comprising a third valve means automatically operable subsequently to the preceding ones to supply pressure fluid to the interior of the die through said second closing means at the moment said die-degassing is completed.

2. A machine according to claim 1, wherein said first closing means is supported by springs urging it to its upper position, spaced apart from said supporting base.

3. A machine according to claim 1, wherein said third valve means is controlled by the lowering of said first closing means.

4. A machine according to claim 1, wherein said second closing means for the die is loosely supported by an arm horizontally movable from an operative position, where the upper closing means of the die overlaps the die, and a second, inoperative position remote from the former, said movable arm being secured to the upper end of a vertical shaft suitably pivoted to the supporting base, to the other end of which a feather means is secured for operating said first and second valve means when the horizontal arm is moved to its operative position.

5. A machine according to claim 4, wherein a vertical pneumatic cylinder is secured to said arm, the second closing means of the die being secured to the piston stem of said cylinder.

6. A machine according to claim 4, wherein a stop means is provided to prevent said movable arm from moving beyond its operative position.

77 A machine according to claim 4, wherein a retaining means is provided for retaining said movable arm at its operative position, said retaining means comprising a ball movable longitudinally of a vertical bore in said feather means, the ball being constantly forced by a spring tending to urge it into a stop seating in the supporting base.

8. A machine according to claim 4, wherein said first and second valve means are operated by said feather means.

9. A machine according to claim 1, wherein two horizontal ears are provided sidewise of and at the median zone of the supporting base, corresponding screws being screwed in said ears and the end of which slightly projecting relative to the lower face of the base for enabling the entire machine to slightly swing.

10. A machine according to claim 1, wherein the pressure fluid circuit is provided with valve means for adjusting the fluid flow. 

1. A machine for producing metal castings using disposable wax dies, comprising a supporting base supporting a first closing means vertically movable between upper and lower positions for supporting and sealing at the bottom a die, a second closing means vertically movable between upper and lower positions for sealing said die at the top and simultaneously urging the first closing means to the lower position, a pneumatic means for operating the second closing means of said die, the first and second closing means being connected, respectively, to a vacuum circuit and a pressure fluid circuit; the machine comprising first and second valve means, respectively, operable to supply vacuum to the first closing means for purposes of degassing said die and to supply pressure fluid to said pneumatic means for operating the second closing means, and also comprising a third valve means automatically operable subsequently to the preceding ones to supply pressure fluid to the interior of the die through said second closing means at the moment said die-degassing is completed.
 2. A machine according to claim 1, wherein said first closing means is supported by springs urging it to its upper position, spaced apart from said supporting base.
 3. A machine according to claim 1, wherein said third valve means is controlled by the lowering of said first closing means.
 4. A machine according to claim 1, wherein said second closing means for the die is loosely supported by an arm horizontally movable from an operative position, where the upper closing means of the die overlaps the die, and a second, inoperative position remote from the former, said movable arm being secured to the upper end of a vertical shaft suitably pivoted to the supporting base, to the other end of which a feather means is secured for operating said first and second valve means when the horizontal arm is moved to its operative position.
 5. A machine according to claim 4, wherein a vertical pneumatic cylinder is secured to said arm, the second closing means of the die being secured to the piston stem of said cylinder.
 6. A machine according to claim 4, wherein a stop means is provided to prevent said movable arm from moving beyond its operative position.
 7. A machine according to claim 4, wherein a retaining means is provided for retaining said movable arm at its operative position, said retaining means comprising a ball movable longitudinally of a vertical bore in said feather means, the ball being constantly forced by a spring tending to urge it into a stop seating in the supporting base.
 8. A machine according to claim 4, wherein said first and second valve means are operated by said feather means.
 9. A machine according to claim 1, wherein two horizontal ears are provided sidewise of and at the median zone of the supporting base, corresponding screws being screwed in said ears and the end of which slightly projecting relative to the lower face of the base for enabling the entire machine to slightly swing.
 10. A machine according to claim 1, wherein the pressure fluid circuit is provided with valve means for adjusting the fluid flow. 